Rechargeable lithium battery

ABSTRACT

Disclosed is a rechargeable lithium battery including a positive electrode including a positive active material; a negative electrode including a negative active material; an electrolyte solution including a lithium salt and a non-aqueous organic solvent; and a separator between the positive and the negative electrodes, the separator including a porous substrate and a coating layer positioned on at least one side of the porous substrate. The negative active material includes a Si-based material; the non-aqueous organic solvent includes cyclic carbonate including ethylene carbonate, propylene carbonate, or combinations thereof, the cyclic carbonate being included in an amount of about 20 volume % to about 60 volume % based on the total amount of the non-aqueous organic solvent; and the coating layer includes a fluorine-based polymer, an inorganic compound, or combinations thereof. The rechargeable lithium battery has improved cycle-life and high temperature storage characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 17/193,371, filed Mar. 5, 2021, which is a divisionalapplication of U.S. patent application Ser. No. 16/105,912, filed Aug.20, 2018, now U.S. Pat. No. 10,978,688, which is a continuation of U.S.patent application Ser. No. 14/303,585, filed Jun. 12, 2014, now U.S.Pat. No. 10,056,594, which claims priority to and the benefit of KoreanPatent Application No. 10-2013-0068436, filed Jun. 14, 2013, the entirecontent of each of which is incorporated herein by reference.

BACKGROUND 1. Field

A rechargeable lithium battery is disclosed.

2. Description of the Related Art

A rechargeable lithium battery typically includes a separator made of aporous film and positioned between positive and negative electrodes, andpores of the film are filled with an electrolyte solution in which alithium salt is dissolved. This rechargeable lithium battery hasimproved characteristics such as high-capacity and high energy density.

However, when the amount of exothermic reactions of the battery isincreased due to the unusual working of the battery, or the positive andthe negative electrodes in the battery are repeatedly contracted andexpanded during charge and discharge cycles, a battery temperature maybe sharply increased. As a result, the separator may become contractedalong with the electrodes or altogether destroyed, thus causing a shortcircuit between the electrodes.

Accordingly, a method of coating the separator with a heat-resistantinorganic particle along with a binder on at least one side to securestability of the battery has been suggested.

However, as the amount of the heat resistance inorganic particle isincreased, the amount of the binder is decreased, and the adherencebetween the separator and the electrode may deteriorate.

SUMMARY

One or more aspects of embodiments of the present invention are directedtowards a rechargeable lithium battery having good adherence between aseparator and an electrode, as well as stability, storability at a hightemperature, good cycle-life characteristics, and the like.

According to one embodiment, a rechargeable lithium battery includes apositive electrode including a positive active material; a negativeelectrode including a negative active material; an electrolyte solutionincluding a lithium salt and a non-aqueous organic solvent; and aseparator positioned between the positive electrode and the negativeelectrode, the separator including a porous substrate and a coatinglayer positioned on at least one side of the porous substrate, whereinthe negative active material includes a Si-based material, thenon-aqueous organic solvent includes a cyclic carbonate includingethylene carbonate, propylene carbonate or combinations thereof, thecyclic carbonate is included in an amount of about 20 volume % to about60 volume % based on the total amount of the non-aqueous organicsolvent, and the coating layer includes a fluorine-based polymer, aninorganic compound, or a combination thereof.

The Si-based material may include Si, silicon oxide, a Si—C composite, asilicon-based alloy, or combinations thereof.

The non-aqueous organic solvent may further include linear carbonateincluding ethylmethyl carbonate, diethyl carbonate, or combinationsthereof.

The electrolyte solution may include an additive, and the additive mayinclude fluoroethylene carbonate, vinylethylene carbonate, propanesultone, succinonitrile, adiponitrile, or combinations thereof.

The additive may be included in an amount of about 5 parts by weight toabout 30 parts by weight based on 100 parts by weight of the non-aqueousorganic solvent.

The porous substrate may include polyethylene, polypropylene, aramid,polyimide, or combinations thereof.

The fluorine-based polymer may include polyvinylidene fluoride (PVdF), apolyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, orcombinations thereof.

The inorganic compound may include Al₂O₃, MgO, TiO₂, Al(OH)₃, Mg(OH)₂,Ti(OH)₄ or combinations thereof.

Accordingly, the present invention may improve battery characteristicsby increasing adherence between the separator and the electrode as wellas securing stability, cycle-life characteristics, storability at a hightemperature, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a rechargeable lithium batteryaccording to one embodiment.

FIG. 2 is a graph showing compression strength results of a gelmanufactured by dissolving materials for preparing a coating layer in anelectrolyte solution of a rechargeable lithium battery according toExample 4.

FIG. 3 is a graph showing adherence results between the negativeelectrode and the separator for a rechargeable lithium battery accordingto Example 4.

FIG. 4 is a graph showing room temperature cycle-life characteristicsresults of rechargeable lithium battery cells according to Examples 2,4, 6, and 8 and Comparative Example 1.

FIG. 5 is a graph showing high temperature storage results of therechargeable lithium battery cells according to Examples 2, 4, 6, and 8and Comparative Example 1.

DETAILED DESCRIPTION

Hereinafter, embodiments are described in detail. However, theseembodiments are exemplary, and this disclosure is not limited thereto.Further, the use of “may” when describing embodiments of the presentinvention refers to “one or more embodiments of the present invention.”

A rechargeable lithium battery according to one embodiment is describedreferring to FIG. 1 .

FIG. 1 is a schematic view showing a rechargeable lithium batteryaccording to one embodiment.

Referring to FIG. 1 , a rechargeable lithium battery 100 according toone embodiment includes an electrode assembly 10, a battery case 20housing the electrode assembly 10, and an electrode tab 13, whichprovides an electrical path for externally leading a current formed inthe electrode assembly 10. Both sides of the battery case 20 may beoverlapped to face each other and sealed together. In addition, anelectrolyte solution may be injected into the battery case 20 housingthe electrode assembly 10.

The electrode assembly 10 may include a positive electrode, a negativeelectrode facing the positive electrode, and a separator positionedbetween the positive and the negative electrodes.

Specifically, the negative electrode may include a current collector anda negative active material layer formed on the current collector, thenegative active material layer including a negative active material.

The negative active material may include a Si-based material. TheSi-based material may be Si, silicon oxide, a Si—C composite, asilicon-based alloy, or combinations thereof. In some embodiments, theSi—C composite is prepared by mixing Si and carbon and includes, forexample, a Si-nano wire and carbon, a Si-nano particle and carbon, andthe like, but is not limited thereto. For example, the silicon-basedalloy can be an alloy of ‘Si’ and ‘an alkali metal, an alkaline-earthmetal, Group 13 to 16 element, a transition metal, a rare earth element,or combinations thereof (except for Si), but embodiments of theinvention are not limited thereto.

The negative active material may be used along with a carbon-basedmaterial, a lithium metal alloy, or combinations thereof.

The carbon-based material may be crystalline carbon, amorphous carbon,or combinations thereof. Non-limiting example of the crystalline carbonincludes a graphite such as a shapeless, sheet-shaped, flake, sphericalshaped or fiber-shaped natural graphite or artificial graphite, andnon-limiting examples of the amorphous carbon include soft carbon orhard carbon, a mesophase pitch carbonized product, fired cokes, and thelike.

The lithium metal alloy may include an alloy of lithium and a metalselected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba,Ra, Ge, Al, and Sn, but embodiments of the invention are not limitedthereto.

In some embodiments, the negative active material layer includes abinder, and optionally a conductive material.

The binder improves binding properties of negative active materialparticles with one another and with a current collector. The binder mayinclude a non-water-soluble binder, a water-soluble binder, or acombination thereof.

Examples of the non-water-soluble binder include polyvinylchloride,carboxylated polyvinylchloride, polyvinylfluoride, an ethyleneoxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, polyamideimide, polyimide, and combinations thereof.

The water-soluble binder includes a styrene-butadiene rubber, anacrylated styrene-butadiene rubber, polyvinyl alcohol, sodiumpolyacrylate, a copolymer including propylene and a C2 to C8 olefin, acopolymer of (meth)acrylic acid and (meth)acrylic acid alkyl ester, or acombination thereof.

When the water-soluble binder is used as a negative electrode binder, acellulose-based compound may be further used to provide viscosity. Thecellulose-based compound includes one or more of carboxymethylcellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkalinemetal salts thereof. The alkaline metal may be sodium (Na), potassium(K), or lithium (Li). The cellulose-based compound may be included in anamount of 0.1 parts by weight to 3 parts by weight based on 100 parts byweight of the negative active material.

In some embodiments, the conductive material improves electricalconductivity of an electrode. Any electrically conductive materialsuitable for use in a rechargeable lithium battery may be used as aconductive material, unless it causes a chemical change in the battery.Non-limiting examples of the conductive material include a carbon-basedmaterial such as natural graphite, artificial graphite, carbon black,acetylene black, ketjen black, a carbon fiber and the like; ametal-based material such as a metal powder or a metal fiber includingcopper, nickel, aluminum, silver, and the like; a conductive polymersuch as a polyphenylene derivative and the like; or a mixture thereof.

The current collector may include a copper foil, a nickel foil, astainless steel foil, a titanium foil, a nickel foam, a copper foam, apolymer substrate coated with a conductive metal, or combinationsthereof.

Hereinafter, the positive electrode according to embodiments of thepresent invention is described.

The positive electrode may include a current collector and a positiveactive material layer formed on the current collector.

The positive active material may include lithiated intercalationcompounds that reversibly intercalate and deintercalate lithium ions. Insome embodiments, at least one composite oxide of lithium and a metalsuch as cobalt, manganese, nickel, or combinations thereof may be used,and non-limiting examples thereof include compounds represented by oneof the following chemical formulae. Li_(a)A_(1-b)R_(b)D₂ (0.90≤a≤1.8 and0≤b≤0.5); Li_(a)E_(1-b)R_(b)O_(2-c)D_(c) (0.90≤a≤1.8, 0≤b≤0.5 and0≤c≤0.05); LiE_(2-b)R_(b)O_(4-c)D_(c) (0≤b≤0.5, 0≤c≤0.05);Li_(a)Ni_(1-b-c)Co_(b)R_(c)D_(α) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and0<α≤2); Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2-α)Z_(a) (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05 and 0<α<2); Li_(a)Ni_(1-b-c)Co_(b)R_(c)O_(2-α)Z₂ (0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05 and 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)R_(c)D_(α)(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05 and 0<α≤2);Li_(a)Ni_(1-b-c)Mn_(b)R_(c)O_(2-α)Z_(α) (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05and 0<α<2); Li_(a)Ni_(1-b-c)Mn_(b)R_(c)O_(2-α)Z₂ (0.90≤a≤1.8, 0≤b≤0.5,0≤c≤0.05 and 0<α<2); Li_(a)Ni_(b)E_(c)G_(d)O₂ (0.90≤a≤1.8, 0≤b≤0.9,0≤c≤0.5 and 0.001≤d≤0.1); Li_(a)Ni_(b)Co_(c)Mn_(d)G_(e)O₂ (0.90≤a≤1.8,0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5 and 0.001≤e≤0.1); Li_(a)NiG_(b)O₂ (0.90≤a≤1.8and 0.001≤b≤0.1); Li_(a)CoG_(b)O₂ (0.90≤a≤1.8 and 0.001≤b≤0.1);Li_(a)MnG_(b)O₂ (0.90≤a≤1.8 and 0.001≤b≤0.1); Li_(a)Mn₂G_(b)O₄(0.90≤a≤1.8 and 0.001≤b≤0.1); QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₅; LiTO₂;LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (0≤f≤2); Li_((3-f))Fe₂(PO₄)₃ (0≤f≤2); andLiFePO₄.

In the above chemical formulae, A is Ni, Co, Mn, or combinationsthereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element,or combinations thereof; D is O, F, S, P, or combinations thereof; E isCo, Mn, or combinations thereof; Z is F, S, P, or combinations thereof;G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; Q isTi, Mo, Mn, or combinations thereof; T is Cr, V, Fe, Sc, Y, orcombinations thereof; and J is V, Cr, Mn, Co, Ni, Cu, or combinationsthereof.

The positive active material layer may include the positive activematerial coated with the coating layer, or a combination of the positiveactive material and the positive active material coated with the coatinglayer. The coating layer may include a compound of a coating element andan oxide of a coating element, a hydroxide of a coating element, anoxyhydroxide of a coating element, an oxycarbonate of a coating element,or a hydroxycarbonate of a coating element. The compound in the coatinglayer may be either amorphous or crystalline. The coating elementincluded in the coating layer may be selected from Mg, Al, Co, K, Na,Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, and a mixture thereof. The coatingprocess may be any conventional coating process as long as it does notcause any side effects on the properties of the positive active material(e.g., spray coating, dipping). Such conventional coating processes arewell known to persons having ordinary skill in this art, so a detaileddescription thereof is omitted.

In some embodiments, the positive active material layer includes abinder and a conductive material.

The binder improves binding properties of positive active materialparticles with one another and with a current collector. Non-limitingexamples of the binder include polyvinyl alcohol, carboxylmethylcellulose, hydroxypropyl cellulose, diacetyl cellulose,polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, anethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, a styrene-butadiene rubber, an acrylatedstyrene-butadiene rubber, an epoxy resin, nylon, and the like, butembodiments of the invention are not limited thereto.

In some embodiments, the conductive material improves conductivity of anelectrode. Any electrically conductive material suitable for use in arechargeable lithium battery may be used as a conductive material,unless it causes a chemical change in the battery. Non-limiting examplesof the conductive material include one or more of natural graphite,artificial graphite, carbon black, acetylene black, ketjen black, acarbon fiber, a metal powder or a metal fiber of copper, nickel,aluminum, silver, and the like, a polyphenylene derivative, and thelike.

The current collector may be Al, but is not limited thereto.

The negative electrode and the positive electrode may be manufactured bya method including mixing each active material, a conductive material,and a binder in a solvent to an active material composition, and coatingthe composition on a current collector. The electrode manufacturingmethod is well known in the art, and thus is not described in detail inthe present specification. The solvent may include N-methylpyrrolidoneand the like, but is not limited thereto. When the water-soluble binderis used in the negative electrode, the solvent may include water.

The electrolyte solution may include a lithium salt and a non-aqueousorganic solvent.

In some embodiments, the non-aqueous organic solvent dissolves thelithium salt, and serves as a medium for transmitting ions taking partin the electrochemical reaction of a battery.

The non-aqueous organic solvent may include a carbonate-based,ester-based, ether-based, ketone-based, alcohol-based, or aproticsolvent. The carbonate-based solvent may include dimethyl carbonate(DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropylcarbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate(EMC), ethylene carbonate (EC), propylene carbonate (PC), butylenecarbonate (BC), and the like. The ester-based solvent may include methylacetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate,methyl propinonate, ethyl propinonate, γ-butyrolactone, decanolide,valerolactone, mevalonolactone, caprolactone, and the like. Theether-based solvent may include dibutyl ether, tetraglyme, diglyme,dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran and the like,and the ketone-based solvent may include cyclohexanone, and the like.The alcohol-based solvent may include ethanol, isopropyl alcohol, andthe like. The aprotic solvent may include nitriles such as R-CN (whereinR is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and mayinclude a double bond, an aromatic ring, or an ether bond), amides suchas dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, andthe like.

The non-aqueous organic solvent may be used alone or in a mixture. Whenthe organic solvent is used in a mixture, the mixture ratio may becontrolled in accordance with a desirable battery performance.

In some embodiments, the non-aqueous organic solvent may include cycliccarbonate including ethylene carbonate, propylene carbonate, orcombinations thereof. In some embodiments, the cyclic carbonate may beincluded in an amount of about 20 volume % to about 60 volume % based onthe total amount of the non-aqueous organic solvent. In otherembodiments, the cyclic carbonate may be included in an amount of about20 volume % to about 55 volume %, about 20 volume % to about 50 volume%, about 20 volume % to about 45 volume % or about 20 volume % to about40 volume % based on the total amount of the non-aqueous organicsolvent.

In certain embodiments, the cyclic carbonate is ethylene carbonate andmay be included in an amount of about 20 volume % to about 60 volume %,20 volume % to about 55 volume %, about 20 volume % to about 50 volume%, about 20 volume % to about 45 volume % or about 20 volume % to about40 volume % based on the total amount of the non-aqueous organicsolvent.

In one embodiment, the carbonate based solvent may include cycliccarbonate and linear carbonate. The linear carbonate may includeethylmethyl carbonate, diethyl carbonate, or combinations thereof.

In some embodiments, the non-aqueous organic solvent may include about20 volume % to about 60 volume % of each of ethylene carbonate (EC),propylene carbonate (PC) or a combination thereof, and about 80 volume %to 40 volume % of ethylmethyl carbonate (EMC), diethyl carbonate (DEC),or a combination thereof. In other embodiments, the non-aqueous organicsolvent may include about 30 volume % to about 50 volume % of ethylenecarbonate (EC), propylene carbonate (PC) or a combination thereof, andabout 70 volume % to 30 volume % of ethylmethyl carbonate (EMC), diethylcarbonate (DEC), or a combination thereof. If the cyclic carbonateincludes both ethylene carbonate (EC) and propylene carbonate (PC) theamount of ethylene carbonate (EC) may be about 10 volume % to about 30volume % and the amount of propylene carbonate (PC) may be about 5volume % to about 30 volume % so that the total amount of propylenecarbonate (PC) and ethylene carbonate (EC) may be about 20 volume % toabout 60 volume % based on the total amount of the non-aqueous organicsolvent. In certain embodiments, the non-aqueous organic solvent mayinclude ethylene carbonate (EC) in an amount of about 25 volume % to 35volume % and propylene carbonate (PC) in an amount about 10 volume % toabout 20 volume % based on the total amount of the non-aqueous organicsolvent. Furthermore, if the linear carbonate includes ethylmethylcarbonate (EMC) and diethyl carbonate (DEC), the amount of ethylmethylcarbonate (EMC) may be about 10 volume % to about 70 volume % and theamount of diethyl carbonate (DEC) may be about 10 volume % to about 70volume % so that the total amount of ethylmethyl carbonate (EMC) anddiethyl carbonate (DEC) may be about 80 volume % to about 40 volume %based on the total amount of the non-aqueous organic solvent. In otherembodiments of the invention wherein the linear carbonate includesethylmethyl carbonate (EMC) and diethyl carbonate (DEC), the amount ofethylmethyl carbonate (EMC) may be about 20 volume % to about 60 volume%, about 25 volume % to about 60 volume %, about 30 volume % to about 60volume %, or about 35 volume % to about 55 volume % and the amount ofdiethyl carbonate (DEC) may be about 10 volume % to about 70 volume %,about 10 volume % to about 60 volume %, about 10 volume % to about 50volume %, about 10 volume % to about 40 volume %, about 20 volume % toabout 40 volume % or about 25 volume % to about 35 volume %, so that thecombined amount of ethylmethyl carbonate (EMC) and diethyl carbonate(DEC) may be about 80 volume % to about 40 volume %, 80 volume % toabout 50 volume %, 80 volume % to about 55 volume %, 80 volume % toabout 60 volume % or 80 volume % to about 70 volume % based on the totalamount of the non-aqueous organic solvent.

When cyclic carbonate is included in an amount of about 20 volume % toabout 60 volume %, about 20 volume % to about 55 volume %, about 20volume % to about 50 volume %, about 20 volume % to about 45 volume % orabout 20 volume % to about 40 volume % based on the total amount of thenon-aqueous organic solvent, a polymer layer coated on the surface ofthe separator may be easily dissolved in an electrolyte solution andthus, may improve compression strength of the separator and adherencebetween the electrode and the separator, and may prevent sharpcontraction and deformation of the separator during charge anddischarge, thus improving cycle-life characteristics of a battery.

The non-aqueous organic solvent may further include an aromatichydrocarbon-based organic solvent as well as the carbonate basedsolvent. In some embodiments, the carbonate-based solvent and thearomatic hydrocarbon-based organic solvent are mixed together in avolume ratio of about 1:1 to about 30:1, about 2:1 to about 30:1, about4:1 to about 30:1, about 6:1 to about 30:1, about 8:1 to about 30:1,about 10:1 to about 30:1, about 15:1 to about 30:1 or about 20:1 toabout 30:1.

The aromatic hydrocarbon-based organic solvent may be an aromatichydrocarbon-based compound represented by the following Chemical Formula1.

In the above Chemical Formula 1, R₁ to R₆ are each independently ahydrogen atom, a halogen, a C1 to C10 alkyl group, a C1 to C10 haloalkylgroup, or combinations thereof.

The aromatic hydrocarbon-based organic solvent may include benzene,fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene,1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene,chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene,1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene,iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene,1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene,1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene,1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene,1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene,1,2,3-trichlorotoluene, 1,2,4-trichlorotoluene, iodotoluene,1,2-diiodotoluene, 1,3-diiodotoluene, 1,4-diiodotoluene,1,2,3-triiodotoluene, 1,2,4-triiodotoluene, xylene, or combinationsthereof.

The non-aqueous organic solvent may further include vinylene carbonateor an ethylene carbonate-based compound represented by the followingChemical Formula 2 in order to improve cycle-life of a battery.

In the above Chemical Formula 2, R₇ and R₈ are each independentlyselected from a hydrogen atom, a halogen, a cyano group (CN), a nitrogroup (NO₂), or a C1 to C5 fluoroalkyl group, provided that at least oneof R₇ and R₈ is a halogen, a cyano group (CN), a nitro group (NO₂), or aC1 to C5 fluoroalkyl group.

Non-limiting examples of the ethylene carbonate-based compound includedifluoro ethylene carbonate, chloroethylene carbonate, dichloroethylenecarbonate, bromoethylene carbonate, dibromoethylene carbonate,nitroethylene carbonate, cyanoethylene carbonate, and the like. Theamount of the vinylene carbonate or the ethylene carbonate-basedcompound used to improve cycle life may be adjusted within anappropriate range.

The electrolyte solution may further include an additive, and theadditive may include fluoroethylene carbonate, vinylethylene carbonate,propane sultone, succinonitrile, adiponitrile, or combinations thereof.In certain embodiments, the additive is fluoroethylene carbonate.

In some embodiments, the additive may be included in an amount of about5 parts by weight to about 30 parts by weight, about 7 parts by weightto about 30 parts by weight, about 10 parts by weight to about 30 partsby weight, about 12 parts by weight to about 30 parts by weight, about15 parts by weight to about 30 parts by weight, about 17 parts by weightto about 30 parts by weight, or about 20 parts by weight to about 30parts by weight based on 100 parts by weight of the non-aqueous organicsolvent.

In embodiments of the present invention wherein the additive isfluoroethylene carbonate, the additive may be included in an amount ofabout 5 parts by weight to about 30 parts, about 7 parts by weight toabout 30 parts by weight, about 10 parts by weight to about 30 parts byweight, about 12 parts by weight to about 30 parts by weight, about 15parts by weight to about 30 parts by weight, about 17 parts by weight toabout 30 parts by weight, or about 20 parts by weight to about 30 partsby weight based on 100 parts by weight of the non-aqueous organicsolvent.

When the additive is included in the non-aqueous organic solvent withinthe described range, the amount of cyclic carbonate may be increased inthe electrolyte solution and, in some embodiments, may cause adecomposition reaction on the surface of an electrode and may form astable passivation film, thus improving cycle-life characteristics of abattery, and flame retardancy of the electrolyte solution, as well asincreasing stability.

In some embodiments, the lithium salt is dissolved in the electrolytesolution in order to operate the rechargeable lithium battery andimprove lithium ion transfer between the positive and the negativeelectrodes by supplying lithium ions in a rechargeable lithium battery.The lithium salt may include at least one supporting salt selected fromLiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiC₄F₉SO₃, LiClO₄, LiAlO₂, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (wherein, x and y are naturalnumbers), LiCl, LiI, LiB(C₂O₄)₂ (lithium bis(oxalato) borate, LiBOB),and combinations thereof. In certain embodiments, the lithium salt mayinclude LiPF₆. The lithium salt may be used in a concentration of about0.1M to about 2.0M, about 0.1 M to about 1.8M, about 0.3M to about 1.8M,about 0.3M to about 1.5M, about 0.5M to about 1.5M, about 0.7M to about1.5M, about 0.7M to about 1.3M, about 1.0M to about 1.3M or about 1.1Mto about 1.2M. In embodiments of the present invention wherein thelithium salt includes LiPF₆, the LiPF₆ may be used in a concentration ofabout 0.1 M to about 2.0M, about 0.1 M to about 1.8M, about 0.3M toabout 1.8M, about 0.3M to about 1.5M, about 0.5M to about 1.5M, about0.7M to about 1.5M, about 0.7M to about 1.3M, about 1.0M to about 1.3Mor about 1.1M to about 1.2M. When the lithium salt is included withinthe above-described concentration range, an electrolyte including anon-aqueous organic solvent, an additive, a lithium salt, and the likemay have appropriate conductivity and viscosity and thus, may improveelectrolyte performance and effectively transfer lithium ions.

Hereinafter, the separator is described, according to one or moreembodiments of the invention.

The separator may be manufactured by a method which includes coating acoating slurry including the fluorine-based polymer, the inorganiccompound, or a combination thereof in a solvent, on at least one surfaceof a porous substrate, and drying the slurry to form a coating layer.The solvent may be acetone, dimethylformamide, N-methylpyrrolidone,cyclohexanone, or a combination thereof.

The fluorine-based polymer may include polyvinylidene fluoride (PVdF), apolyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer, orcombinations thereof. In another embodiment, the fluorine-based polymermay be a mixture of first and second binder polymers having a differentparticle size, or a solvent-soluble binder polymer or an emulsion binderpolymer.

The concentration of coating slurry may be controlled in order to havean amount of the fluorine-based polymer of about 1 g/m² to 3 g/m² in thecoating layer, or in order to have an amount of the mixed fluorine-basedpolymer and the inorganic compound of about 2 g/m 2 to 6 g/m² in thecoating layer.

The drying of the slurry may include, for example, hot air drying, UVdrying, and the like, at a drying rate of about 30%/min to about70%/min.

In embodiments of the present invention, the drying rate of about30%/min to about 70%/min indicates a speed at which about 30% to about70% of a solvent included in the slurry per one minute is dried and maybe determined based on the drying temperature, supplied air amount,discharged air amount, wind speed, heating method, and the like.

When the drying is performed within the drying rate range, a crack on ordeformation of the surface may be prevented, and the binder polymer mayalso sufficiently move toward the surface.

In some embodiments, the drying may be performed at a drying rate ofabout 40%/min to about 60%/min within the range.

The drying temperature may be determined by various factors such as atype of solvent and atmosphere conditions during the drying. The dryingtemperature may be in a range from about 45° C. to about 110° C., and insome embodiments from about 50° C. to about 90° C., and in someembodiments from about 60° C. to about 80° C. When the drying isperformed within the temperature range, the solvent may be removedwithout excessive contraction of a porous substrate.

In an embodiment of the present invention, the separator is locatedbetween the positive electrode and the negative electrode, and includesa porous substrate and a coating layer positioned on at least one sideof the porous substrate, the coating layer including a fluorine-basedpolymer, an inorganic compound, or combinations thereof.

In an embodiment of the present invention, the porous substrate includespolyethylene, polypropylene, aramid, polyimide, or combinations thereof.

When the porous substrate is polyethylene, polypropylene, aramid,polyimide, or combinations thereof, the coating layer may be easilycoated thereon.

In some embodiments, the fluorine-based polymer includes polyvinylidenefluoride (PVdF), a polyvinylidene fluoride-hexafluoropropylene(PVdF-HFP) copolymer, or combinations thereof.

In some embodiments, the inorganic compound includes Al₂O₃, MgO, TiO₂,Al(OH)₃, Mg(OH)₂, Ti(OH)₄ or combinations thereof.

According to some embodiments, the separator has improved adherence whenusing the coating layer including fluorine-based polymer, inorganiccompound, or combinations thereof and thus, may be more stably boundwith an electrode in a pouch-type battery using a flexible packingmaterial such as a lamination film and the like, and may preventdetachment of the electrode from the separator and generation of a gaptherebetween.

In addition, the fluorine-based polymer, inorganic compound, orcombinations thereof may be more easily dispersed in the electrolytesolution composition and may form a polymer gel, thus preventing sharpcontraction or deformation of the separator during charge/discharge andimproving cycle-life characteristics of a battery.

An entire thickness of the separator may be determined based on thecapacity of the battery. For example, the separator may have a thicknessranging from about 10 μm to about 30 μm. A polymer coating layer mayhave a thickness of about 0.1 μm to about 5 μm on one side of theseparator. When the polymer coating layer has a smaller thickness thanthe range, sufficient heat resistance may not be obtained. Furthermore,when the polymer coating layer has a larger thickness than the range,the polymer coating layer may increase the overall thickness of theseparator and thus, may decrease battery capacity.

The separator manufactured using the method according to embodiments ofthe present invention separates the positive electrode from the negativeelectrode and provides a path for lithium ions, [and its detaileddescription is the same as described above].

Hereinafter, a rechargeable lithium battery including the aforementionedpositive electrode, negative electrode, electrolyte solution, andseparator is illustrated, according to one or more embodiments of thepresent invention.

Rechargeable lithium batteries may be classified as lithium ionbatteries, lithium ion polymer batteries, and lithium polymer batteriesaccording to the presence of a separator and the kind of electrolyteused in the battery. The rechargeable lithium batteries may also beclassified as cylindrical, prismatic, coin-type, or pouch-type batteriesaccording to shapes, and may be classified as thin film or bulkbatteries. According to one embodiment, a rechargeable lithium batterymay be a pouch-type battery. Structures and manufacturing methods forlithium ion batteries pertaining to this disclosure are well known inthe art.

Hereinafter, the present disclosure is illustrated in more detail withreference to examples. However, these examples are exemplary, and thepresent disclosure is not limited thereto.

Example 1

97.0 wt % of LiCoO₂ as a positive active material, 1 wt % of denka blackas a conductive material, and 2 wt % of polyvinylidene fluoride (PVdF)as a binder were added to an N-methylpyrrolidone (NMP) solvent,preparing a positive active material composition. The positive activematerial composition was coated on an aluminum (Al) thin film, dried,and roll-pressed, manufacturing a positive electrode.

(2) 97 wt % of a negative active material (3 wt % of SiO_(x) (x is in arange of 1.0 to 1.5)+97 wt % of Graphite), 1 wt % of carboxylmethylcellulose as a thickener, and 2 wt % of a styrene-butadiene rubber as abinder were added to distilled water, preparing a negative activematerial composition. The negative active material composition wascoated on a copper foil, dried, and roll-pressed, manufacturing anegative electrode.

(3) An electrolyte solution was prepared by mixing ethylene carbonate(EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC) in avolume ratio of 20:50:30 and adding 1.15M LiPF₆ and 5 parts by weight offluoroethylene carbonate (FEC) (based on 100 parts by weight of themixed solvent) to the mixed solvent.

(4) Polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) copolymer wasdissolved in acetone, and the solution was gravure-coated on both sidesof a 9 μm-thick polyethylene (PE) separator. Thereafter, the resultantwas dried at a temperature of 75° C. at a drying rate of about 50%/min,to produce a separator with a PVdF coating layer. The coating layer was1.5 μm-thick on each side, and had an amount of polyvinylidenefluoride-hexafluoropropylene of 2 g/m².

(5) The positive electrode, the negative electrode, and the separatorwere manufactured into an electrode assembly, the electrode assembly wasput in a battery case, the electrolyte solution was injected into thebattery case, and the battery case was sealed and charged up to 3.8 V toform a film on the negative electrode.

Subsequently, a pouch-type battery cell was manufactured by performing aheat-pressing process to gelate a PVdF layer on the separator and toclosely adhere the separator to the substrate and then, a vacuum-sealingprocess.

Example 2

A pouch-type battery cell was manufactured according to the same methodas Example 1 except for mixing ethylene carbonate, ethylmethylcarbonate, and diethyl carbonate in a volume ratio of 30:40:30 insteadof 20:50:30.

Example 3

A pouch-type battery cell was manufactured according to the same methodas Example 2 except for using fluoroethylene carbonate (FEC) in anamount of 7 parts by weight instead of 5 parts by weight.

Example 4

A pouch-type battery cell was manufactured according to the same methodas Example 2 except for using fluoroethylene carbonate (FEC) in anamount of 10 parts by weight instead of 5 parts by weight.

Example 5

A pouch-type battery cell was manufactured according to the same methodas Example 2 except for using fluoroethylene carbonate (FEC) in anamount of 15 parts by weight instead of 5 parts by weight.

Example 6

A pouch-type battery cell was manufactured according to the same methodas Example 2 except for using fluoroethylene carbonate (FEC) in anamount of 20 parts by weight instead of 5 parts by weight.

Example 7

A pouch-type battery cell was manufactured according to the same methodas Example 2 except for using fluoroethylene carbonate (FEC) in anamount of 30 parts by weight instead of 5 parts by weight.

Example 8

A pouch-type battery cell was manufactured according to the same methodas Example 1 except for mixing the ethylene carbonate, propylenecarbonate, ethylmethyl carbonate, and diethyl carbonate in a volumeratio of 30:15:25:30 instead of mixing ethylene carbonate, ethylmethylcarbonate and diethyl carbonate in a volume ratio of 20:50:30 and usingthe fluoroethylene carbonate in an amount of 10 parts by weight insteadof 5 parts by weight.

Comparative Example 1

A pouch-type battery cell was manufactured according to the same methodas Example 1 except for mixing the ethylene carbonate, ethylmethylcarbonate, and diethyl carbonate in a volume ratio of 10:60:30 insteadof 20:50:30.

Comparative Example 2

A pouch-type battery cell was manufactured according to the same methodas Example 1 except for using a polyethylene separator having no coatinglayer.

Evaluation 1: Compression Strength Evaluation

The electrolyte solutions according to Examples 1 to 8 and ComparativeExample 1 and 1.5 wt % of PVdF powder were weighed and placed in theirrespective vials. The mixtures were put in a 100° C. oven to dissolvethe PVdF, and the solutions were cooled down to room temperature,preparing cylindrical gels having a diameter of 20 mm and a height of 15mm.

The obtained gels were positioned between upper and lower anvils in aproperty tester (Instron 3344) and compressed to a break point at aspeed of 100 mm/min and then, measured regarding compression strength.The compression strength measurement results are provided in thefollowing Table 1 and FIG. 2 .

FIG. 2 shows compression strength depending on compression distance whenthe gel including the electrolyte solution according to Example 4 wascompressed to a break point.

As shown in Table 1 and FIG. 2 , the gels including the electrolytesolution according to Examples 1 to 8 showed improved compressionstrength compared with those of the gels including the electrolytesolution according to Comparative Examples

Evaluation 2: Adherence Evaluation

After putting a negative electrode and the 45 mm-wide and 60 mm-longseparator according to each of the Examples 1 to 8 and ComparativeExample 1 in a pouch container and respectively injecting eachelectrolyte solution according to Examples 1 to 8 and ComparativeExample 1, the negative electrode and the separator were impregnated inthe electrolyte solution and heat-pressed and then, adherencetherebetween was evaluated by performing a peeling test at a speed of 10mm/min with a property tester, Instron 3344.

The obtained results were converted into strength per a unit width(N/mm) based on the peeling strength (N) relative to the width direction(45 mm) of a specimen.

The adherence measurement results are provided in the following Table 1and FIG. 3 .

FIG. 3 shows the result of the electrolyte solution according to Example4.

As shown in Table 1 and FIG. 3 , the electrolyte solutions according toExamples 1 to 8 resulted in more improved adherence between the negativeelectrode and the separator than the electrolyte solution according toComparative Example 1. The reason is that the appropriate electrolytesolution composition according to the present invention improvedadherence between a PVdF component coated on the separator and thenegative electrode.

TABLE 1 Lithium Additive Electrolyte solution salt (part by Compression(vol %) (M) weight) strength Adherence EC PC EMC DEC LiPF₆ FEC (MPa)(N/mm) Example 1 20 0 50 30 1.15 5 1.64 0.007 Example 2 30 0 40 30 1.155 1.76 0.009 Example 3 30 0 40 30 1.15 7 1.79 0.010 Example 4 30 0 40 301.15 10 1.84 0.013 Example 5 30 0 40 30 1.15 15 1.89 0.015 Example 6 300 40 30 1.15 20 1.95 0.018 Example 7 30 0 40 30 1.15 30 2.11 0.025Example 8 30 15 25 30 1.15 10 2.03 0.021 Comparative 10 0 60 30 1.15 51.38 0.003 Example 1

Evaluation 3: Room Temperature Cycle-life Evaluation

The cells according to Examples 1 to 8 and Comparative Examples 1 and 2(capacity: 1C=1600 mAh) were 350 times charged and discharged under thefollowing conditions, and capacity retention of the cells was obtainedas a percentage % based on capacity of the cells at the first cycle.

Charge: 0.7C/4.3V of a CC-CV condition, 0.025C cut-off

Discharge: 0.5C of a CC condition, 3.0V cut-off

The room temperature cycle-life evaluation results are provided in thefollowing Table 2 and FIG. 4 .

FIG. 4 shows the results of Examples 2, 4, 6, 8, and Comparative Example1.

As shown in the following Table 2 and FIG. 4 , the cells includingcyclic carbonate in a higher amount and a coating layer according toExamples 1 to 8 showed improved cycle-life characteristics compared withthe cell including cyclic carbonate in a lower amount according toComparative Example 1 and the cell including no coating layer accordingto Comparative Example 2, and accordingly, higher amounts offluoroethylene carbonate in the same electrolyte solution compositionmay bring about better cycle-life.

According to some embodiments, the fluoroethylene carbonate plays a roleof forming a film on a negative electrode as an additive thus improvingcycle-life of the battery. In addition, it belongs to cyclic carbonatesand may improve the cycle-life of the battery when larger amounts areincluded.

Since cyclic carbonate has high solubility in PVdF, the more cycliccarbonate is included, the higher solubility in PVdF it has.Accordingly, the cyclic carbonate may have a positive influence onimproving compression strength and adherence between the electrode andthe separator.

The cell according to Example 8 included more cyclic carbonate than thecells according to Examples 4 to 7 but showed slightly deterioratedcycle-life due to high viscosity of ethylene carbonate and propylenecarbonate.

Evaluation 4: High Temperature Storage Evaluation

The cells according to Examples 1 to 8 and Comparative Examples 1 andComparative Example 2 were under a CC-CV condition of 0.7C/4.3V and acut-off condition of 0.025C and then, were evaluated regarding storageat 60° C. for 30 days, and increases in thickness of the cells weremeasured every 5 days to calculate a battery swelling degree as apercentage %.

The high temperature storage evaluation results are provided in thefollowing Table 2 and FIG. 5 .

FIG. 5 shows the high temperature storage evaluation results of thecells according to Examples 2, 4, 6, and 8 and Comparative Example 1.

As shown in the following Table 2 and FIG. 5 , the cells includingcyclic carbonate in a higher amount according to Examples 1 to 8 showedhigher adherence between the electrode and the separator than the cellincluding cyclic carbonate in a lower amount according to ComparativeExample 1 and thus, were not easily deformed by gas generated duringstorage at a high temperature and showed improved storage characteristicat a high temperature. In addition, the cells including a coating layeraccording to Examples 1 to 8 showed better high temperature storagecharacteristics than the cell including no coating layer according toComparative Example 2.

TABLE 2 Room High Lithium Additive temperature temperature Electrolytesolution salt (parts cycle-life storage (vol %) (M) by weight) (% after350 (% after EC PC EMC DEC LiPF₆ FEC times) 30 days) Example 1 20 0 5030 1.15 5 72.7 19.0 Example 2 30 0 40 30 1.15 5 81.0 17.3 Example 3 30 040 30 1.15 7 82.3 11.2 Example 4 30 0 40 30 1.15 10 86.2 10.3 Example 530 0 40 30 1.15 15 86.4 10.7 Example 6 30 0 40 30 1.15 20 86.8 11.4Example 7 30 0 40 30 1.15 30 87.4 13.5 Example 8 30 15 25 30 1.15 1084.9 9.4 Comparative 10 0 60 30 1.15 5 NG 20.5 Example 1 Comparative 300 40 30 1.15 10 NG 27.3 Example 2

Based on Evaluations 1 to 4, cycle-life and high temperature storagecharacteristics of a cell may be improved by appropriately adjusting anelectrolyte solution composition and the amounts of fluoroethylenecarbonate.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims and equivalents thereof.

What is claimed is:
 1. A rechargeable lithium battery comprising: apositive electrode comprising a positive active material; a negativeelectrode comprising a negative active material; an electrolyte solutioncomprising a lithium salt, a non-aqueous organic solvent, and anadditive, the non-aqueous organic solvent comprising a carbonate; and aseparator between the positive electrode and the negative electrode, theseparator comprising a porous substrate and a coating layer on at leastone side of the porous substrate, wherein the coating layer comprises apolymer, an inorganic compound, or a combination thereof, and wherein anadherence between the negative electrode and the separator is about0.007 N/mm to 0.025 N/mm.
 2. The rechargeable lithium battery of claim1, wherein the separator has a compression strength evaluation of about1.64 MPa to about 2.11 MPa.
 3. The rechargeable lithium battery of claim1, wherein the carbonate comprises a cyclic carbonate and a linearcarbonate, and the cyclic carbonate is included in an amount of about 20volume % to about 60 volume % based on a total amount of the non-aqueousorganic solvent.
 4. The rechargeable lithium battery of claim 3, whereinthe linear carbonate comprises ethylmethyl carbonate and dimethylcarbonate.
 5. The rechargeable lithium battery of claim 4, wherein anamount of the linear carbonate comprising ethylmethyl carbonate anddimethyl carbonate is at least about 40 volume % based on the totalamount of the non-aqueous organic solvent.
 6. The rechargeable lithiumbattery of claim 4, wherein an amount of ethylmethyl carbonate is about10 volume % to about 70 volume % based on the total amount of thenon-aqueous organic solvent.
 7. The rechargeable lithium battery ofclaim 4, wherein an amount of dimethyl carbonate is about 10 volume % toabout 70 volume % based on the total amount of the non-aqueous organicsolvent.
 8. The rechargeable lithium battery of claim 1, wherein thepolymer comprises a fluorine-based polymer.
 9. The rechargeable lithiumbattery of claim 1, wherein the inorganic compound comprises Al(aluminum).
 10. The rechargeable lithium battery of claim 9, wherein theinorganic compound comprises Al₂O₃, Al(OH)₃ or combinations thereof. 11.The rechargeable lithium battery of claim 1, wherein the poroussubstrate comprises polyethylene, polypropylene, aramid, or acombination thereof.
 12. The rechargeable lithium battery of claim 1,wherein the additive is in an amount of about 5 parts by weight to about30 parts by weight based on 100 parts by weight of the non-aqueousorganic solvent.
 13. The rechargeable lithium battery of claim 1,wherein the additive comprises fluoroethylene carbonate.
 14. Therechargeable lithium battery of claim 1, wherein the separator has athickness from about 10 μm to about 30 μm.
 15. The rechargeable lithiumbattery of claim 1, wherein the coating layer further comprisespolyvinylidene fluoride.
 16. The rechargeable lithium battery of claim1, wherein the battery is a pouch-type battery.
 17. The rechargeablelithium battery of claim 1, wherein the battery is a cylindricalbattery.
 18. The rechargeable lithium battery of claim 1, wherein thenegative active material comprises a carbon-based material.
 19. Therechargeable lithium battery of claim 1, further comprising apassivation film between the negative electrode and the separator, thepassivation film being derived from the additive in an amount of about 5parts by weight to about 30 parts by weight based on 100 parts by weightof the non-aqueous organic solvent.
 20. The rechargeable lithium batteryof claim 1, wherein the positive active material comprises anickel-included compound selected from Li_(a)Ni_(b)E_(c)G_(d)O₂(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5 and 0.001≤d≤0.1, E is Co; G is Al, Cr, Mn,Fe, Mg, La, Ce, Sr, V, or combinations thereof).